[PATCH V2] mkimage: fit: Do not tail-pad fitImage with external data

[Tom Rini]

On Tue, May 05, 2020 at 07:59:24PM +0200, Marek Vasut wrote:
> On 5/5/20 7:55 PM, Tom Rini wrote:
> > On Tue, May 05, 2020 at 07:53:42PM +0200, Marek Vasut wrote:
> >> On 5/5/20 7:50 PM, Tom Rini wrote:
> >>> On Tue, May 05, 2020 at 06:39:58PM +0200, Marek Vasut wrote:
> >>>> On 5/5/20 6:37 PM, Alex Kiernan wrote:
> >>>>> On Tue, May 5, 2020 at 2:28 PM Marek Vasut <marex at denx.de> wrote:
> >>>>>>
> >>>>>> On 5/5/20 3:22 PM, Alex Kiernan wrote:
> >>>>>>> On Mon, May 4, 2020 at 12:28 PM Tom Rini <trini at konsulko.com> wrote:
> >>>>>>>>
> >>>>>>>> On Fri, May 01, 2020 at 05:40:25PM +0200, Marek Vasut wrote:
> >>>>>>>>
> >>>>>>>>> There is no reason to tail-pad fitImage with external data to 4-bytes,
> >>>>>>>>> while fitImage without external data does not have any such padding and
> >>>>>>>>> is often unaligned. DT spec also does not mandate any such padding.
> >>>>>>>>>
> >>>>>>>>> Moreover, the tail-pad fills the last few bytes with uninitialized data,
> >>>>>>>>> which could lead to a potential information leak.
> >>>>>>>>>
> >>>>>>>>> $ echo -n xy > /tmp/data ; \
> >>>>>>>>>       ./tools/mkimage -E -f auto -d /tmp/data /tmp/fitImage ; \
> >>>>>>>>>       hexdump -vC /tmp/fitImage | tail -n 3
> >>>>>>>>>
> >>>>>>>>> before:
> >>>>>>>>> 00000260  61 2d 6f 66 66 73 65 74  00 64 61 74 61 2d 73 69  |a-offset.data-si|
> >>>>>>>>> 00000270  7a 65 00 00 78 79 64 64                           |ze..xydd|
> >>>>>>>>>                    ^^       ^^ ^^
> >>>>>>>>> after:
> >>>>>>>>> 00000260  61 2d 6f 66 66 73 65 74  00 64 61 74 61 2d 73 69  |a-offset.data-si|
> >>>>>>>>> 00000270  7a 65 00 78 79                                    |ze.xy|
> >>>>>>>>>
> >>>>>>>>> Signed-off-by: Marek Vasut <marex at denx.de>
> >>>>>>>>> Reviewed-by: Simon Glass <sjg at chromium.org>
> >>>>>>>>> Cc: Heinrich Schuchardt <xypron.glpk at gmx.de>
> >>>>>>>>> Cc: Tom Rini <trini at konsulko.com>
> >>>>>>>>
> >>>>>>>> Applied to u-boot/master, thanks!
> >>>>>>>>
> >>>>>>>
> >>>>>>> This breaks booting on my board (am3352, eMMC boot, FIT u-boot,
> >>>>>>> CONFIG_SPL_LOAD_FIT). Not got any useful diagnostics - if I boot it
> >>>>>>> from eMMC I get nothing at all on the console, if I boot over ymodem
> >>>>>>> it stalls at 420k, before continuing to 460k. My guess is there's some
> >>>>>>> error going to the console at the 420k mark, but obviously it's lost
> >>>>>>> in the ymodem... I have two DTBs in the FIT image, 420k would about
> >>>>>>> align to the point between them.
> >>>>>>
> >>>>>> My bet would be on some padding / unaligned access problem that this
> >>>>>> patch uncovered. Can you take a look ?
> >>>>>
> >>>>> Seems plausible. With this change my external data starts at 0x483 and
> >>>>> everything after it is non-aligned:
> >>>>
> >>>> Should the beginning of external data be aligned ?
> >>>
> >>> If in U-Boot we revert e8c2d25845c72c7202a628a97d45e31beea40668 does the
> >>> problem go away?  If so, that's not a fix outright, it means we need to
> >>> dig back in to the libfdt thread and find the "make this work without
> >>> killing performance everywhere all the time" option.
> >>
> >> Still, my question is, should the beginning of external data be aligned
> >> ? And if so, to what, 4 bytes like FDT entries OR 8 bytes to cater for
> >> arm64/rv64 ?
> > 
> > Is "external data" the kernel in this case?  If so, I swear Linux
> > mandates 8 byte alignment for arm32 as well.
> 
> External data can be anything, and if it is supposed to be 8 bytes, we
> already failed at that since forever.

I would be entirely unsurprised at things working through a combination
of luck and co-incidence in our previous padding working out.  So, what
typically is "external data" in this context?

-- 
Tom
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